The main purpose of the proposed work is to identify neural and endocrine mechanisms underlying circannual rhythms of reproduction and body weight in the golden-mantled ground squirrel. Specific projects include: (1) Evalution of the role of the pineal gland in the development, generation and expression of circannual reproductive rhythms. (2) Documentation of the function of the suprachiasmatic nuclei in the generation of circannual reproductive cycles. (3) Elaboration of relations between circadian and circannual clocks, in particular the degree of overlap in neural mechanisms for circadian activity and circannual reproductive and body weight cycles. (4) Description of the role of ovarian and testicular hormones in the expression and modulation of circannual body weight cycles. (5) Evaluation of the pineal gland as a putative driving circadian oscillator. (6) Assessment of the functional status of extraretinal photoreception during exposure of diurnal squirrels to direct bright sunlight. (7) Analysis of the circannual organization of the neuroendocrine axis by long-term sequential measurement of gonadotrophins in individual gonadectomized squirrels. Parameters to be measured include body weight, food intake, wheel-running activity, morphological and physiological indices of reproductive status, steroid hormone and gonadotrophin levels in plasma.